polar start starts then stops

A truck I recently bought came with a Polar Start model PS2705 (i think). When I hit the middle (start) button, the truck starts and runs for about 5 seconds then shuts off. It then repeats this 2 more times before it gives up. I've tried all the basic key combinations I've been able to find on other sites to reset the system but no luck. Idle mode seems to function properly allowing me to remove the key from the truck when its already running but no luck on the auto start. Does anyone have any idea how I could fix this? It's starting to get cold here and I'm gonna need this soon. Thanks in advance.

Sorry for the lack of detail... the "truck" is a 2002 GMC Envoy XL. So you mean this signal needs to be sent from the vehicle to the Polar Start unit, or is it vice versa? If so, how do I go about tracing the ECU/PCM signal. How would I locate/identify the correct wire?

Sounds like the unit has lost its tach signal. Check to see that the purple wire for the unit is hooked up to the white wire off the ECM on the drivers side of the motor. The white wire is in the blue plug of the ECM. Then program the remote starter's tach as follows. The procedures for tach adjustment are as follows: 1. Hold hood switch down for 6 seconds. 2. Release pinswitch (parking lights should come on) 3. With parking lights on, immediately push and release pinswitch again. 4. Parking lights will stay on for up to 20 seconds (if not repeat from step 1). 5. With lights on press Channel 3 (Trunk) of remote transmitter at the same time. (lights will flash 1 to 7 times) 6. Start the vehicle using the key. 7. If lights stay on, then you have selected an incorrect tach wire. (relocate tach wire and start from step 1) If lights go off then proceed to the next step. 8. Allow vehicle to reach regular engine idle speed, then press and release the brakes. (parking lights will flash appropriate setting, from 1 to 7 flashes) 9. Press Channel 3 (Trunk) of remote transmitter, to save setting. (Parking lights will flash one long flash)sparky